wordpress css file

Try to use relative URLs to your imported css files. So try to remove first / from each import URL:

@import url('styles/forms.css');
@import url('styles/tables.css');
@import url('styles/homepage.css');
@import url('styles/reset.css');
@import url('styles/stimenu.css');
@import url('styles/layout.css');
@import url('styles/demo.css');

Also pay attention to the fact that using @import directives is bad practice and strongly not recommended to use. Use link instead of it. Why? Read here: @import vs link.

So in your I strongly recommend you write your code like this:

add_action( 'wp_enqueue_scripts', 'wpse8170_enqueue_scripts' );
function wpse8170_enqueue_scripts() {
    $baseurl = get_template_directory_uri(); // if you write plugin use plugins_url();

    wp_enqueue_style( 'wpse8170-forms', "{$baseurl}/styles/forms.css" );
    wp_enqueue_style( 'wpse8170-tables', "{$baseurl}/styles/tables.css" );
    wp_enqueue_style( 'wpse8170-homepage', "{$baseurl}/styles/homepage.css" );
    wp_enqueue_style( 'wpse8170-reset', "{$baseurl}/styles/reset.css" );
    wp_enqueue_style( 'wpse8170-stimenu', "{$baseurl}/styles/stimenu.css" );
    wp_enqueue_style( 'wpse8170-layout', "{$baseurl}/styles/layout.css" );
    wp_enqueue_style( 'wpse8170-demo', "{$baseurl}/styles/demo.css" );

    wp_enqueue_style( 'wpse8170-style', "{$baseurl}/style.css", array( 'wpse8170-forms', 'wpse8170-tables', 'wpse8170-homepage', 'wpse8170-reset', 'wpse8170-stimenu', 'wpse8170-layout', 'wpse8170-demo' ) );
}